A storage apparatus is coupled to an external apparatus such as a host computer via a communication network. The storage apparatus of this type includes, for example, multiple hard disk drives (HDD) as storage devices for storing data. For the purpose of reducing costs required for storage media, data volume reduction processing is performed in the course of storing data into a storage device. The reduction of data volume is done through file compression or de-duplication. The file compression reduces the data volume by compressing data segments having identical data within a single file. On the other hand, the de-duplication reduces the total data volume in a file system or a storage system by detecting data segments having identical data not only within a single file but also among files and by compressing the detected data segments.
In the following description, a “chunk” denotes a unit-data segment that is a unit for de-duplication. In addition, a “container” denotes a set of data consisting of two or more chunks. In general, chunks closely related to each other are gathered in a container for efficient execution of the de-duplication. Moreover, a “container index” denotes a table created for each container and including records of hash values calculated for the respective chunks stored in the container. In addition, a “content” denotes a logically-grouped set of data that is a unit for storage in the storage device. Types of contents include not only general files, but also an aggregate of general files, such as an archive file, a backup file and a virtual volume file.
For storing a content into a storage apparatus from a host computer via a communication network, there have been proposed techniques of performing efficient data storage processing through reduction in a data transfer volume by making redundancy determination in advance as to whether each chunk is already stored in the storage apparatus and by sending only chunks determined as not stored. These techniques are described in Patent Literatures 1 and 2, for example.